Thermostatic switch



Nov. 14, 1950 F. L HoLLls'rER 2,529,941

THERIDSTATIC SWITCH F'ld Aug. 12, 1946 l t @530 19m/26 f7 j? 9 '1339 36 'l g l A ZZ -E up .l

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..1 wwf/W02 'jflHOLLISTER Patented Nov. 14, 1950 Application August 12, 1946, Serial No. 689,901 In Great Britain August 13, 1945 (Cl. 20o-137)v 13 claims. l

The present invention comprises improvements in or relating to electric current switches and relates more particularly to such switches in which a rapid make or break of a current circuit is desired with only a small relative movement between the switch contacts. The latter feature yis particularly desired in switches for the operation ot which mechanical movements of only small extent are available, as for example in thermostat switches for controlling the supply of electric current to heating or refrigerating apparatus in which it is desired to maintain a substantially uniform temperature.

It is an object of the invention to provide a switch of the nature iirst described above which is satisfactory in operation and compact in structure.

According to the invention an electric current switch comprises a lever carrying a movable switch contact and a magnetic armature for effecting operation of the lever, and spring means to eiIect a reverse operation of the lever mounted to afford one part to be subject to an operating force and a second part to transmit an opposite resilient pressure on an armof the lever.

According to the invention also an electric current switch, for example, a switch as described in the last preceding paragraph, comprises a lever which carries a movable switch contact and a magnetic armature for effecting operation of the lever and which is of channel section, and spring means to 'effect a reverse operation of the lever housed within the channel aorded thereby.

Preferably an electric current switch constructed in accordance with the invention comprises a magnetic keeper mounted to ail'ord a supplementary shunt path for magnetic iiux for spark quenching on separation of the contacts.

According to one constructional example of the invention the lever has a pivotal mounting serving also to support a spring having one arm to be subject to an operating force and a. second arm formed with a return bowed portion secured to an arm of the lever.

In order that the invention may be more clearly understood a preferred constructional example will be described with reference to the accompanying drawings in which:

Figure 1 is a side elevation, partly in section, of a switch for effecting thermostatic control of electrical heating apparatus,

Figure 2 is a top plan view of the switch shown in Figure 1 with the outer cover removed,

Figure 3 is an end elevation, as seen from the right, of the switch shown in Figure 2,

Figure 4 is a section, as seen in the direction of the arrows, on the line 4-4 of Figure 2, and

Figure 5 is a section on an enlarged scale, as seen in the direction of the arrows, on the line 5--5 of Figure 2.

Like reference numerals 'are employed to denote like parts in the various iigures or the -drawings.

The switch shown in the drawings, as will be seen more particularly from the side elevation in Figure 1, has attached thereto a. temperature responsive device for securing automatic operation of the switch. This device comprises a brass tube I0 secured to the base plate II and rigidly secured internally of the brass tube at its lower end by brazing, solder or the like I2 is an invar bar I3 having an upper end, seen more clearly in Figures 3 to 5, projecting through an aperture in the base plate II free from contact withl the latter.A The rod type temperature sensitive element shown is conveniently enclosed in a cylindrical casing I4 secured by the set screw I5 with the interposition of an insulating washer I6 between the base plate Il and casing I4. The thermosensitive element and casing are intended to be immersed,

for example in a hot water storage tank, screwthread Il being employed to effect a suitable mounting on the wall of the tank so that the actual switch described hereinafter is located externally and closely adjacent the wall of the tank.

The base plate I l is conveniently of brass and vhas a terminal I8 for an electrical earth connection secured to it. A pair of screwthreaded pillars I8 are mounted in the base plate and surrounded at their base by brass distance pieces 2l and annular insulators 2| of any preferred insulating material. The insulators 2| are surmounted by a brass bracket 22 affording a supporting cradle between thel pillars but offset laterally from them as seen in Figure l. The bracket 22 is 'again surmounted by perforated arms of a permanent magnet 23, further annular insulators 24, a brass cross member 25 which is laterally oii'set from the pillars I9 in a direction opposite to the oiiset supporting cradle 22, annular insulators 26 and screwthreaded brass securing nuts 21 of disc form having slots or grooves 28 (Figure 2) for engagement by a suitable tool for tightening. The switch mechanism is normally enclosed by a rectangular cover or box 29 conveniently built up from plates of synthetic plastic material or produced as an integrally formed moulding. The cover 29 (Figure l) is perforated to receive the ends of the pillars I9 and is secured in position by nuts 30 screwatraen threaded on the pillars. The cover 29 is dlmen sioned to iit on the base plate ii at its free edges while the inner surface of the top oi the cover is in contact with the retaining discs 2l. Signe cg'eki; 29 is "i ed apair of screws 0 w c take mgrrwtlibgded apertures respectively provided in a lug 3l depending from the cross member and a bracket 32 upstanding from a xed insulating support 33 secured to the base plate il and located so that the cover 29 nts snugly between the earthing terminal connection la and insulating support 33.

The screws i3() afford or are secured to a, pair of current supply lead connections, the cross member 25 having secured to it a suitably coated copper switch contact 94. having a screwthreaded shank 35 secured by the nut 36. The contact 3d is located substantially between the poles of the horse-shoe magnet 23 which are shaped to form a partial shroud for the contact, while a shaped soft iron keeper 3l is also secured to theV cross member 25 to eii'ect a more complete magnetic shrouding of the switch contacts. The similar co-operating switch contact 3&3 is superimposed on an armature 3S subject to the action of the magnet and carried with the contact @t at one end of a channel section lever du pivotally carried by a pair of pivots il mounted in the supporting cradle 22, as will be seen more clearly from Figures 3 and 5, and passing through the side anges of the lever '138. A further smaller short channel section member 42 is located within the channel section of the lever and also pivotally mounted on the pivots All. A pair of insulating plates dit disposed in the channel member d2 embrace a dat spring strip 44 one end of which is secured to a lateral base extension l5 (Figure d) of the upstanding bracket-32 on the insulating support b3. The spring strip passes substantially through the axis of the pivots (li and is formed at its other end with a return bowed portion et secured to the underside of the arm of the lever du remotefrom the switch contacts 34 and 38, the latter being conveniently enclosed in a shrouding mica tube 4l. The spring strip acts as a current conductor from the lever 40 and contact 38 to one terminal connection 30. The mica tube al enables the magnet poles and keeper 3l to be placed closely together so that an etfective shunt or diverter path for magnetic iiux is provided when the switch contacts are separated.

The switch contacts are normally held in engagement by the action of attraction of the magnet 23 on armature 39 but rocking of the lever y 40 to break this engagement is effected by pressure on the extended arm of the spring strip N. In the present construction of switch for thermostatic control of electrical heating apparatus the movable member I3 of the temperature sensitive device is secured to a frame piece 4B carrying a depending rod 49 passing through an aperture in the lever 40 to bear against the upper insulating plate 43 in a position displaced from the axis of the pivots 4|. Expansion of the brass tube I0 causes pressure by the rod 9 on the spring 44 to rock the lever 40 and separate the contacts u and 38 to interrupt the supply of heating current. The latter will normally be an alternating current mains supply and the keeper 3l affords a supplementary shunt or diversion path for magnetic flux when the switch contacts and the armature and magnet poles are separated. Such a shunt path aids in spark quenching by acting as a magnetic blow out. In addition the speed of the make and break is arranged to be such as to be complete within a current half cycle period to prevent re-establlshment 0f an arc after the current surge reaches a zerol value. Uniform operation of the switch is secured due to absence of serious distortion in the form of spring which is adopted. Movements to effect operation of the switch and the separation of the contacts are in all cases very small, and to limit the travel of the lever du the anges are shaped at its forward or contact end to act as a limiting stop by engagement with the base extension 45 of the bracket 32. The construction which has been described may have parts formed or die cast from other metal, such as aluminium, or may have many parts formed from moulded plastic material which also gives satisfactory insulation. Modification of the construction provided in accordance with the invention is also possible, for example by the inclusion of a dash-pot or like device for damping the movement of the switch to secure a time lag in its operation under the influence of the magnet. A hand or :finger operated lever may also be provided either in addition 0r in place of the temperature sensitive control, the said lever operating a suitable cam or intermediate lever for exerting an operating pressure on the spring strip. Any form of remote control of the operation o the switch may be adapted and control of the operation of the switch may be effected by means other than a temperature sensitive device such as by fluid pressure, e. g. with the use of compressed air 0r a Bourdon tube device, or by a water level control or electromagnetic control.

In the specic example of thermostatic control switch described above, it is found convenient tor the control of electrically operated refrigerators to arrange for a temperature sensitive device to exert an upward push on the spring element @it on that side of the pivots di remote from the switch contacts to secure the opening of the latter. Adjustment of the temperature of'operation of the Aconstruction of thermostat switch which is shown in the drawings is eiected by adjustment of the rod 49 which is carried by the screw 5| having a slot for engagement by an adjusting tool. The latter screw is carried in an internally screwthreaded collar having a head 50 and secured in the bridge or stirrup piece 48. If desired a rotatable partmay be carried externally of the casing 29 and secured on an extension of the screw 5l, so that the said rotatable part may be adjusted to a position giving a desired temperature control, by adjustment of an indicating mark on the rotatable part to an appropriate position on a temperature scale inscribed on the casing 29.

In the use of the thermostat switch which has been described for effecting a control of the operation of an electric cooker or oven, the device shown in Figure 1 is conveniently mounted at a forward upper corner of the oven. The terminal connections as well as the earth lead are then preferably carried by the base member Il and the casing 29 carried on the base H to be rotatable relatively thereto. The casing 29 is then of cylindrical form enclosing the switch mechanism and has a knurled periphery projecting through a suitable aperture in the front casing of the oven for manipulation in accordance with actual temperature indications inscribed on the cover or on a drum or ring rotatable therewith and visible through a second aperture in the front casing of the oven. The casing 29 is then secured to a screw, such as 5 screw 5l but having a coarser thread than the latter, serving to adjust the position of the switch operating rod 49.

I claim:

1. An electric switch of the character described comprising a stationary contract, supporting means for said stationary contact, a movable contact, a channel lever carrying said contact, a support pivotally carrying said lever, a magnetic armature for effecting operation of said lever, magnetic means adjacent said contacts to afford a supplementary shunt path for magnetic flux for spark quenching on separation of said contacts, spring means for actuating said lever, and a pivoted insulated cradle support for said spring, said pivoted insulated cradle support being housed together with said lever within the channel conilnes thereof. i

2. An electric switch as claimed in claim 1 characterized by the fact that a terminal connection is provided to which one arm of said spring is secured.

3. An electric switch of the character described comprising a base plate, upstanding pillars therefrom, a stationary contact, a cross support carrying said stationary contact intermediate said upstanding pillars and carried thereby, a movable contact, a channel lever carrying said movable contact, a support pivotally carrying said lever, a magnetic armature for effecting operation of said lever, magnetic means adjacent said contacts to aiord a supplementary shunt path for magnetic flux for spark quenching on separation of said contacts, spring means for actuating said lever, and a pivoted insulated cradle support between said upstanding pillars for said spring means, said pivoted insulated cradle support being housed together with said lever within the channel contines thereof.

4. An electric switch as claimed in claim 3 characterized by the fact that said cross member carries a magnetic keeper for said magnetic means ucarried by said upstanding pillars.

5. An electric switch of the character described comprising a stationary contact, supporting means for said stationary contact, a movable contact, a channel lever carrying said contact and having an opening therethrough, a support pivotally carrying said lever, a magnetic armature for eiecting operation of said lever, magr netic means adjacent said contacts to afford a supplementary shunt path for magnetic ilux for spark quenching on separation of said contacts, spring means for actuating said lever, a pivoted insulated cradle support for said spring, said pivoted insulated cradle support being housed tosether with said lever within the channel confines thereof, and a stirrup surrounding said lever and spring means for connection to a temperature sensitive element, said stirrup having an abutment to engage a portion of said spring means at a point free from contact with said lever by passing through the opening thereof.

6. An electric switch of the character described comprising a stationary contact, supporting means for said stationary contact, a movable contact, a magnetic armature, a lever carrying said movable contact and said magnetic armature, a support pivotallycarrying said lever, magnetic means adjacent said contacts to aord a supplemental shunt path for magnetic flux for spark quenching on separation of said contacts, spring means for actuating said lever, and a pivoted insulated cradle support for said spring means.

'1. An electric switch as claimed in claim 6 characterized by the fact that said magnetic means is a permanent magnet arranged with said stationary contact to co-operate with said magnetic armature carried by said lever to effect operation of said lever in one direction.

8. An electric switch as claimed in claim 6 wherein said spring means is mounted to be subject to and to transmit an operating force to actuate said lever and said movable contact in opposition to said magnetic means.

9. An electric switch as claimed in claim 6 characterized by the fact that said spring means comprises a resilient leaf extending between a fixed anchorage and said pivot adapted to be rocked by movement of said leaf.

10. An electric switch of the character described comprising a stationary contact, supporting means for said stationary contact, a movable contact, a magnetic armature, a channel lever carrying said movable contact and said magnetic armature, an insulated cradle pivot support for carrying said channel lever, and a leaf spring one end of which is extended beyond said pivot and secured to said lever and the other end of which is secured to said support means, said leaf spring being pivoted coaxially with said lever and housed within the channel confines of said channel lever.

11. An electric switch of the character described comprising a stationary contact, supporting means for said stationary contact, a movable contact, a magnetic armature, a channel lever carrying said movable contact and said magnetic armature, a pivot support for carrying said lever, an insulated cradle carrying said pivot support, and a leaf spring connected between said pivot and said contact carrying lever to transmit an opposite movement to that of said leaf spring to one end oi' said lever to actuate said lever and said switch contacts.

12. An electric switch as claimed in claim 11 wherein said leaf spring and said channel lever will coaxially pivot, said leaf spring being within the confines of the walls of said channel lever.

13. An electric switch as claimed in claim 11 characterized by the fact that said spring leaf extends beyond said pivot to afford a return radius secured to said channel lever.

FREDERICK LOUIS HOILIS'IER.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS 60 Number Name Date 1,123,277 Haagn Jan. 5, 1915 1,398,635 Fogwell et al Nov. 29, 1921 1,681,346 Sawyer Mar. 6, 1928 1,914,675 Satchwell June 20, 1933 6 2,183,745 Huber Dec. 19, 1939 2,314,989 Kercher Mar. 30, 1943 FOREIGN PATENTS Number Country Date 482,002 Great Britain Mar. 22, 1938 

